With rapid development of circuit integration, Radio Frequency RF circuits tend to be integrated and modular, which is particularly beneficial to mobile User Equipment UE miniaturization. An RF circuit of an existing mobile UE (such as a cellphone) consists of an RF integrated circuit as a core and of peripheral auxiliary and control circuits. The RF integrated circuit, as the main part of the mobile UE RF circuit, may include a signal receiving circuit and a signal transmitting circuit. The signal receiving circuit may include an antenna, a Surface Acoustic Wave SAW filter, a Low Noise Amplifier LNA, a mixer, an Intermediate-Frequency IF filter, an IF amplifier, etc.
When a mobile UE receives a signal, the signal sent out by a base station BS managing a cell, such as a Global System of Mobile communication GSM 900 MHz signal, is transmitted to an antenna end of the mobile UE via a wireless interface. The signal may enter the SAW through the antenna, where any out-of-band signal and noise may be filtered out. The filtered signal may enter the LNA to be amplified. The LNA-amplified signal may be sent to the mixer, where the LNA-amplified signal may be mixed with a Local Oscillator LO signal output by a Voltage Controlled Oscillator VCO, producing an IF signal. The IF signal is sent through the IF filter, such that any out-of-band noise may be filtered out. Then, the filtered IF signal may be sent to the IF amplifier, where the filtered IF signal may be amplified. Then, the output signal may enter an In-phase/Quadrature I/Q demodulator, where the output signal is demodulated. The demodulated I/Q signal may be sent to a baseband part, where digital processing is performed on the demodulated I/Q signal.
In an existing mobile UE, in order to allow a receiver thereof to receive signals in different frequency bands, such as GSM 900 MHz and GSM 1800 MHz, a receiving circuit is designed respectively for receiving signals in each frequency band. Such parallel receiving circuits are then integrated into one overall integrated circuit. In addition, an antenna switch is added at a rear end of an antenna, to transfer a received signal respectively to a receiving circuit corresponding to a frequency band of the received signal. On this basis, in order to allow the receiver of a mobile UE to receive signals in different modes, such as signals in GSM 800 MHz/1900 MHz and in Time Division-Synchronous Code Division Multiple Access TD-SCDMA 1880 MHz-1920 MHz, a receiving circuit may further be designed respectively for receiving signals in each mode.
As an RF circuit adopts Time Division Multiplexing, receiving and transmitting will not be performed at the same time, front ends of receiving circuits for receiving same-band signals in different modes are completely equivalent. Therefore, for same-band signals in different modes, receiving circuit front ends inside the integrated circuit may be used repeatedly, which may lead to multiple equivalent RF chips in the integrated circuit, increasing an area and cost in circuit design.